possible deadlock in cpuhp_thread_fun

Status: upstream: reported on 2026/10/26 10:19
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+a265816368571f78ab88@syzkaller.appspotmail.com
First crash: 4d14h, last: 4d14h
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
f47b20cb repro-c Reproduced: ✅ ❓ possible deadlock in cpuhp_thread_fun 2026/10/26 01:40 2026/10/26 01:40 2026/10/26 04:11 1d9ca40b
26b5716e repro-c 💥 possible deadlock in cpuhp_thread_fun 2026/10/25 00:03 2026/10/25 00:03 2026/10/25 05:27 1d9ca40b
691bda1c assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ❌ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in cpuhp_thread_fun 2026/10/24 07:48 2026/10/24 07:48 2026/10/24 08:02 1d9ca40b
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernel?] possible deadlock in cpuhp_thread_fun 0 (1) 2026/10/26 10:19
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/10/26 04:12 13m retest repro git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 21a7f44fd0765fcc5194130b28767786eba1d1e7 no crash job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
cpuhp/1/26 is trying to acquire lock:
ffffffff90e24aa0 (device_links_lock){+.+.}-{4:4}, at: device_links_write_lock drivers/base/core.c:322 [inline]
ffffffff90e24aa0 (device_links_lock){+.+.}-{4:4}, at: device_links_purge drivers/base/core.c:1704 [inline]
ffffffff90e24aa0 (device_links_lock){+.+.}-{4:4}, at: device_del+0x3d7/0x9b0 drivers/base/core.c:3969

but task is already holding lock:
ffffffff8fc7de00 (cpuhp_state-down){+.+.}-{0:0}, at: lockdep_acquire_cpus_lock kernel/cpu.c:545 [inline]
ffffffff8fc7de00 (cpuhp_state-down){+.+.}-{0:0}, at: cpuhp_thread_fun+0xdd/0x7c0 kernel/cpu.c:1085

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (cpuhp_state-down){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       cpuhp_lock_acquire kernel/cpu.c:103 [inline]
       cpuhp_kick_ap_work+0xa4/0xbd0 kernel/cpu.c:1188
       _cpu_down+0x47d/0x1020 kernel/cpu.c:1436
       cpu_down_maps_locked kernel/cpu.c:1483 [inline]
       cpu_down kernel/cpu.c:1491 [inline]
       cpu_device_down+0x82/0xc0 kernel/cpu.c:1508
       device_offline drivers/base/core.c:4283 [inline]
       device_offline+0x2f4/0x400 drivers/base/core.c:4267
       acpi_bus_offline+0x3c7/0x550 drivers/acpi/scan.c:164
       acpi_scan_try_to_offline drivers/acpi/scan.c:227 [inline]
       acpi_scan_hot_remove drivers/acpi/scan.c:329 [inline]
       acpi_generic_hotplug_event drivers/acpi/scan.c:432 [inline]
       acpi_device_hotplug+0x627/0xbe0 drivers/acpi/scan.c:456
       acpi_hotplug_work_fn+0x5e/0x90 drivers/acpi/osl.c:1194
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (cpu_hotplug_lock){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       percpu_down_write+0x4e/0x3d0 kernel/locking/percpu-rwsem.c:232
       cpus_write_lock kernel/cpu.c:508 [inline]
       _cpu_up+0x68/0x960 kernel/cpu.c:1622
       cpu_up+0x1ba/0x230 kernel/cpu.c:1706
       cpuhp_bringup_mask+0xf8/0x180 kernel/cpu.c:1772
       cpuhp_bringup_cpus_parallel kernel/cpu.c:1850 [inline]
       bringup_nonboot_cpus+0xd9/0x1b0 kernel/cpu.c:1876
       smp_init+0x32/0x150 kernel/smp.c:1151
       kernel_init_freeable+0x44b/0x7b0 init/main.c:1667
       kernel_init+0x21/0x1e0 init/main.c:1565
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (cpu_add_remove_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19f/0x1c10 kernel/locking/mutex.c:821
       cpu_maps_update_begin kernel/cpu.c:468 [inline]
       cpu_down kernel/cpu.c:1490 [inline]
       cpu_device_down+0x46/0xc0 kernel/cpu.c:1508
       device_offline drivers/base/core.c:4283 [inline]
       device_offline+0x2f4/0x400 drivers/base/core.c:4267
       acpi_bus_offline+0x3c7/0x550 drivers/acpi/scan.c:164
       acpi_scan_try_to_offline drivers/acpi/scan.c:227 [inline]
       acpi_scan_hot_remove drivers/acpi/scan.c:329 [inline]
       acpi_generic_hotplug_event drivers/acpi/scan.c:432 [inline]
       acpi_device_hotplug+0x627/0xbe0 drivers/acpi/scan.c:456
       acpi_hotplug_work_fn+0x5e/0x90 drivers/acpi/osl.c:1194
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&device->physical_node_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19f/0x1c10 kernel/locking/mutex.c:821
       class_mutex_constructor include/linux/mutex.h:253 [inline]
       acpi_primary_dev_companion drivers/acpi/bus.c:817 [inline]
       acpi_companion_match+0xc0/0x180 drivers/acpi/bus.c:873
       acpi_device_uevent_modalias+0x19/0x30 drivers/acpi/device_sysfs.c:280
       platform_uevent+0x51/0xc0 drivers/base/platform.c:1473
       dev_uevent+0x1de/0x870 drivers/base/core.c:2766
       kobject_uevent_env+0x6eb/0x18b0 lib/kobject_uevent.c:576
       kobject_synth_uevent+0x6f0/0x7d0 lib/kobject_uevent.c:207
       uevent_store+0x24/0x50 drivers/base/core.c:2847
       dev_attr_store+0x58/0x80 drivers/base/core.c:2509
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6af/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (kn->active#5){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       kernfs_drain+0x4eb/0x600 fs/kernfs/dir.c:534
       __kernfs_remove+0x34c/0xbc0 fs/kernfs/dir.c:1578
       kernfs_remove_by_name_ns+0x7c/0x120 fs/kernfs/dir.c:1796
       sysfs_remove_file include/linux/sysfs.h:780 [inline]
       device_remove_file drivers/base/core.c:3146 [inline]
       device_remove_file drivers/base/core.c:3142 [inline]
       device_del+0x361/0x9b0 drivers/base/core.c:3963
       device_unregister+0x1d/0xe0 drivers/base/core.c:4006
       kref_put include/linux/kref.h:65 [inline]
       device_link_put_kref drivers/base/core.c:1022 [inline]
       device_link_put_kref+0x156/0x1b0 drivers/base/core.c:1019
       device_link_remove+0xbb/0x110 drivers/base/core.c:1065
       destroy_regulator+0x417/0x510 drivers/regulator/core.c:2647
       _regulator_put+0xf2/0x1b0 drivers/regulator/core.c:2679
       regulator_put+0x23/0x30 drivers/regulator/core.c:2696
       release_nodes+0xa5/0x120 drivers/base/devres.c:546
       devres_release_group+0x1c2/0x2d0 drivers/base/devres.c:739
       i2c_device_probe+0x70c/0xd10 drivers/i2c/i2c-core-base.c:612
       call_driver_probe drivers/base/dd.c:628 [inline]
       really_probe+0x241/0xa60 drivers/base/dd.c:706
       __driver_probe_device+0x210/0x460 drivers/base/dd.c:868
       driver_probe_device+0x4a/0x140 drivers/base/dd.c:898
       __device_attach_driver+0x1df/0x320 drivers/base/dd.c:1026
       bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:500
       __device_attach+0x1e4/0x4d0 drivers/base/dd.c:1098
       device_initial_probe+0xaf/0xd0 drivers/base/dd.c:1153
       bus_probe_device+0x64/0x160 drivers/base/bus.c:620
       device_add+0x121d/0x1970 drivers/base/core.c:3776
       i2c_new_client_device+0x660/0xd30 drivers/i2c/i2c-core-base.c:1020
       new_device_store+0x20f/0x420 drivers/i2c/i2c-core-base.c:1308
       dev_attr_store+0x58/0x80 drivers/base/core.c:2509
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6af/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (device_links_lock){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19f/0x1c10 kernel/locking/mutex.c:821
       device_links_write_lock drivers/base/core.c:322 [inline]
       device_links_purge drivers/base/core.c:1704 [inline]
       device_del+0x3d7/0x9b0 drivers/base/core.c:3969
       device_unregister+0x1d/0xe0 drivers/base/core.c:4006
       mce_device_remove arch/x86/kernel/cpu/mce/core.c:2715 [inline]
       mce_cpu_pre_down+0x325/0x620 arch/x86/kernel/cpu/mce/core.c:2776
       cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
       cpuhp_thread_fun+0x3e9/0x7c0 kernel/cpu.c:1109
       smpboot_thread_fn+0x41f/0xb90 kernel/smpboot.c:162
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  device_links_lock --> cpu_hotplug_lock --> cpuhp_state-down

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(cpuhp_state-down);
                               lock(cpu_hotplug_lock);
                               lock(cpuhp_state-down);
  lock(device_links_lock);

 *** DEADLOCK ***

locks held by cpuhp/1/26: 2, last CPU#1:
 #0: ffffffff8fc7b810 (cpu_hotplug_lock){++++}-{0:0}, at: lockdep_acquire_cpus_lock kernel/cpu.c:545 [inline]
 #0: ffffffff8fc7b810 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0xdd/0x7c0 kernel/cpu.c:1085
 #1: ffffffff8fc7de00 (cpuhp_state-down){+.+.}-{0:0}, at: lockdep_acquire_cpus_lock kernel/cpu.c:545 [inline]
 #1: ffffffff8fc7de00 (cpuhp_state-down){+.+.}-{0:0}, at: cpuhp_thread_fun+0xdd/0x7c0 kernel/cpu.c:1085

stack backtrace:
CPU: 1 UID: 0 PID: 26 Comm: cpuhp/1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19f/0x1c10 kernel/locking/mutex.c:821
 device_links_write_lock drivers/base/core.c:322 [inline]
 device_links_purge drivers/base/core.c:1704 [inline]
 device_del+0x3d7/0x9b0 drivers/base/core.c:3969
 device_unregister+0x1d/0xe0 drivers/base/core.c:4006
 mce_device_remove arch/x86/kernel/cpu/mce/core.c:2715 [inline]
 mce_cpu_pre_down+0x325/0x620 arch/x86/kernel/cpu/mce/core.c:2776
 cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
 cpuhp_thread_fun+0x3e9/0x7c0 kernel/cpu.c:1109
 smpboot_thread_fn+0x41f/0xb90 kernel/smpboot.c:162
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/22 10:07 upstream 4df4d2a577db 4ba27f85 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in cpuhp_thread_fun
* Struck through repros no longer work on HEAD.